Smart meters monitor the use of utilities, e.g., electricity, heat, gas and water, by a consumer. Typically, the smart meter communicates with a utility provider via network or grid, which can include, perhaps, millions of smart meters. Smart meters can turn utilities on or off, record usage information, detect service outages, unauthorized use, control utility consumption, and manage payments.
Smart meters must reliably and securely communicate with utility providers. Wired or wireless mesh network can be used. A number of protocols are known, e.g., ANSI C12.18, ANSI C12.19, and ANSI C12.21 for optical communications, as well as IEEE 802.15.4, IEEE P1901.2, and 802.11. The European Union uses IEC 61107 and IEC 62056. In Japan, the Energy Conservation is involved in promoting smart metering, as well as public and private utilities.
Smart meters can be connected to utility providers via one or more concentrators. The concentrators receive metering information from the smart meters, and forward the information to the providers for controlling or monitoring the utilities. The concentrator can also transmit control packets to smart meters for management purposes.
Smart meters can be equipped with lower power and lossy transceivers, such as ZigBee radios, and are deployed in a relatively large geometric region, e.g., entire counties. Therefore, smart meters and concentrators form a large scale wireless network, in which the concentrators maintain the network.
In such a large scale wireless network, data packets have to be relayed from a source node (source) to a destination node (destination) by multiple hop communications unless the source and the destination node are one-hop neighbors. Therefore, optimal routing of the packets is of primary importance, because the network requires high reliability and low latency for both metering information and control packet transmission.
A number of routing methods in mobile ad-hoc networks and wireless sensor networks are known. However, most methods are designed for point-to-point communications in relatively small networks, and therefore are not suited for smart meter networks in which there are only a few dedicated data concentrators.
One routing method is the Routing Protocol for Low Power and Lossy Networks (RPL), which is under development by the Internet Engineering Task Force (IETF). RPL is designed for large scale low power and lossy networks, such as smart meter networks.
In RPL, nodes are organized into one or more Destination Oriented Directed Acyclic Graphs (DODAG). Within a DODAG, a single destination node is the root of DODAG, and the DODAG root node (concentrators) collects the information generated in the network, and routes the information outside of the network, when necessary. RPL constructs and maintains the DODAG structure using DODAG Information Object (DIO) packets, which specify necessary parameters as configured from, and controlled by a policy at the DODAG root.
A rank is one of parameters in the DIO packet for DODAG construction and maintenance. The rank of a node defines a position of the node relative to other nodes with respect to a DODAG root. Each node maintains its own rank. The DODAG root node has the lowest rank of all the node's in the DODAG. Nodes maintain their ranks based on a parent-child relationship in which a child must have a rank strictly greater than all ranks of its parents. The DODAG root node has no parent.
A node can receive multiple DIO packets from neighboring nodes within the same DODAG.
To join a DODAG, the node selects a subset of the DIO packet transmitters as its parents, and determines its rank using an objective (cost) function. Among all its parents, the node selects one parent as its preferred parent to be used as the next hop node along upward routes to the concentrators.
It is assumed that smart meters are not energy-constrained. Instead, electric meters have hardware and communication capacity constraints that are primarily determined by cost, and secondarily by power consumption. As a result, deployments can vary significantly in terms of memory size, computation power and communication capabilities. For this reason, the use of RPL storing or non-storing mode is deployment specific.
When smart meters are memory constrained and cannot adequately store the route tables necessary to support hop-by-hop routing, RPL non-storing mode is preferred. If the nodes are capable of storing such routing tables, then the use of the storing mode may lead to reduced overhead and route repair latency. However, in high-density environments, storing routes can be challenging.
Therefore, RPL support of downward routes is determined by a Mode of Operation (MOP) in the DIO packet. The MOP is configured by the DODAG root, and cannot be changed by other nodes.
The MOP has three options so that the RPL cannot allow downward route or support downward routes with storing mode in which downward routes using in-network routing tables or support downward routes with non-storing mode in which downward routes using source routing from DODAG roots.
The directed acyclic structure is the key in the RPL. The acyclic structure is guaranteed as long as the rank of any node is strictly greater than all ranks of its parent nodes. It is safe for a node to decrease its rank, as long as its new rank remains greater than all ranks of its parents. However, increasing the rank can cause routing loops within the DODAG.
In conventional networks, a broken link can cause a loop. After the broken link detected, a node can advertise a rank of infinity. If this infinity rank advertisement is lost, then other nodes do not receive the advertisement and a packet circulates through the loop ad infinitum.
Though RPL provides a mechanism for resolving loops; it is known that the mechanism can cause even greater problems than the routing loop itself.
Therefore, it is desirable to provide a rank computation method for loop-free routing in smart meter networks with broken links. It is also desirable to provide a local DODAG repair method that does not create any loop.